The present invention is generally directed to conveyor belt assemblies used to transport materials from one location to another. Conventional conveyor belt assemblies typically include an endless loop-type conveyor belt, wherein at least one end of the belt is supported by a shaft-mounted pulley having an adjustable position. The pulley shaft is adjustable in a manner that increases or decreases the amount of tension applied to the conveyor belt. The assembly used to adjust the position of the shaft is referred to as a "take-up frame."
Generally, take-up frames of the prior art have assumed one of several configurations. For example, in one common embodiment, the take-up frame includes a pair of opposing bearings mounted to respective ends of a pulley shaft. Each of the bearings are secured to a bearing block which is slidably supported by a corresponding frame member positioned adjacent to the conveyor belt. The bearing block is movable within the frame member in a direction perpendicular to the shaft. Each of the bearing blocks are held in place at a particular position within the frame member by a take-up screw. By rotating the take-up screw and moving the position of the bearing block, greater or lesser tension can be placed on the conveyor belt. Such conventional take-up frames are disclosed, for instance, in U.S. Pat. No. 2,791,474 to Richard and in U.S. Pat. No. 4,212,502 to Ames et al.
These "screw-type" take-up frames are generally configured to place the pulley shaft in a set position. Thus, the take-up frame will not compensate for expansion and contraction of the belt due to temperature fluctuations or for other reasons. Insufficient tension or excess tension placed on the belt can sometimes lead to belt slippage, belt misalignment, or other undesirable effects.
In addition, "screw-type" take-up frames also cannot readily counteract the effect of shock loading. Shock loading occurs when a foreign object, such as a rock, tool or other object, travels on the return side of the belt and gets caught between the belt and one of the pulleys, causing a substantial increase in tension on the belt. Shock loading can damage the belt and the components of the take-up frame assembly itself.
Various attempts have been made to create a take-up frame that will compensate for the above described irregularities that may occur when the conveyor belt is running. For instance, Bryant Products, Inc. of Ashippun, Wis. markets a take-up frame known as the TELESCOPER. This particular take-up frame employs a spring that applies a force to a pulley shaft supporting a conveyor belt. The spring compensates for some fluctuations that occur as the conveyor is moving. By incorporating a spring, the take-up frame applies greater tension to the conveyor belt as the spring is compressed.
Previously, the assignee of the present invention built and sold a take-up frame assembly designed specifically to cushion the stresses placed on a conveyor belt caused by a chain drive. The take-up frame assembly included a bearing and bearing block connected to a hydraulic cylinder. The hydraulic cylinder was placed in communication with an accumulator. In this arrangement, the hydraulic cylinder acted much like a spring.
Although the above-discussed prior art has provided great advances in take-up frames for conveyor belt assemblies, there is room for further improvement. In particular, a need exists for a take-up frame that maintains a conveyor belt under substantially constant tension, even during conveyor belt expansion or contraction or during shock loading. The present invention is directed to improved take-up frame assemblies that not only place a conveyor belt under substantially constant tension, but also provide a means for gauging the amount of tension in the belt.